The present invention relates to methods useful in treating subterranean formations. More particularly, the present invention relates to methods of coating particulates that may be used in subterranean operations with a resin and a tackifier.
Often subterranean formations are subjected to treatments that insert particulates at or near a production zone. One such treatment is hydraulic fracturing. In hydraulic fracturing treatments, a viscous fracturing fluid, which also functions as a carrier fluid, is pumped into a producing zone to be fractured at a rate and pressure such that one or more fractures are formed in the zone. Particulate solids commonly referred to in the art as “proppant,” are commonly suspended in a portion of the fracturing fluid so that the proppant is deposited in the fractures. The proppant deposited in the fractures functions to prevent the fractures from fully closing so that conductive channels are formed through which produced hydrocarbons may flow. Generally, the force of the formation bearing down on the proppant acts to keep the proppant in place. However, it is often the case that not all of the proppant will be effectively trapped by the pressure of the formation. For instance, some proppant particulates may break free of the proppant pack with the force of the produced fluids, or some portion of the proppant particulates may crush under the pressure of the formation and create unconsolidated particulates.
Gravel packs may also act to add particulates into a portion of a subterranean formation. A “gravel pack” is a term commonly used to refer to a volume of particulate materials (such as sand) placed into a well bore to at least partially reduce the migration of unconsolidated formation particulates into the well bore. Gravel packing operations commonly involve placing a gravel pack screen in the well bore neighboring a desired portion of the subterranean formation, and packing the surrounding annulus between the screen and the subterranean formation with particulate materials that are sized to prevent and inhibit the passage of formation solids through the gravel pack with produced fluids. In some instances, a screenless gravel packing operation may be performed. In either case, the resulting structure presents a barrier to migrating formation particles, and stabilizes the formation, while still permitting fluid flow. The gravel, among other things, is designed to prevent the particulates from occluding the screen or migrating with the produced fluids, and the screen acts to prevent the gravel from entering the well bore. However, it is possible for gravel to escape from the confines of the pack or for the gravel pack to bridge or otherwise fail to fully halt the flow of unconsolidated particulates into the well bore.
In some situations, hydraulic fracturing and gravel packing operations may be combined into a single treatment. Such treatments are often referred to as “frac pack” operations. In some cases, the treatments are generally completed with a gravel pack screen assembly in place with the hydraulic fracturing treatment being pumped through the annular space between the casing and screen. In this situation, the hydraulic fracturing treatment ends in a screen-out condition, creating an annular gravel pack between the screen and casing. In other cases, the fracturing treatment may be performed prior to installing the screen and placing a gravel pack.
Particulates (such as proppant or gravel) used in subterranean operations are often coated with resins to facilitate consolidation of the particulates and/or to prevent their subsequent flow-back through the conductive channels in the subterranean formation, which can, for example, clog the conductive channels and/or damage the interior of the formation or equipment. The term “resin” as used herein refers to any of numerous physically similar polymerized synthetics or chemically modified natural resins including thermoplastic materials and thermosetting materials. In addition to maintaining a relatively solids-free production stream, consolidating particulates also aids in protecting the conductivity of the formation. Flow of unconsolidated particulate material through the conductive channels in a subterranean formation may tend to clog the conductive channels and/or damage the interior of the formation or may erode downhole equipment, plug piping and vessels, and cause damage to valves, instruments and other production equipment. For these among other reasons, it is desirable to consolidate unconsolidated particulates within a producing zone in a subterranean formation.